How 18th Century Technology Could Down an Airliner

While the mystery of what caused Air France Flight 447 to vanish into the Atlantic Ocean is far from solved, preliminary reports suggest equipment first developed in the 18th century may have contributed to the crash of one of the most sophisticated airliners ever built.

The air speed indicators on the doomed plane included a Pitot tube, named for Henri Pitot, the French engineer who in 1732 created an instrument that could measure the velocity of a fluid. Grossly oversimplified, airspeed is determined by measuring the difference between ram air pressure coming into the Pitot tube and static air pressure at altitude. If anything blocks a Pitot tube or static port, the measurement will be inaccurate and jeopardize the safety of the flight. That’s a Pitot tube of a small plane in the photo.

If an iced-over Pitot tube had anything to do with the tragedy of Flight 447, it wouldn’t be the first time. At least two other accidents in recent memory were attributed to blocked tubes.

Fans of the Canadian TV show Mayday! (aired in the U.S. as “Air Emergency”) may be familiar with Birgenair Flight 301, a 1996 discount charter flight from Puerta Plata, Dominican Republic that never reached its final destination of Frankfurt, Germany. Flight 301, a Boeing 757, crashed shortly after takeoff, killing all 189 people on board.

An investigation of Flight 301 showed that a faulty ASI engaged the autopilot to reduce power, sending the aircraft into a stall before the crew could recover. Though none of the Pitot tubes were recovered, investigators theorize that one of the tubes was blocked by a wasp nest, most likely built while the plane sat for nearly a month without flying.

In 1996, Aeroperu Flight 603 crashed after a blocked static port kept in-flight instruments from functioning properly. Without proper altitude readings, the crew of the aircraft, another Boeing 757, could not determine altitude and crashed into the Pacific Ocean while attempting an emergency landing.

The cause of the crash was found to be a static port blocked by a piece of masking tape, left on by a maintenance worker. The accident resulted in a $29 million lawsuit.

While there is no definitive evidence that faulty ASI caused the crash of Flight 447, the airline had already begun changing ASIs for improved versions in late April — albeit not on the doomed aircraft. The AP obtained a memo from a French pilots’ union which urged Air France pilots not to fly A330 and A340 aircraft that have not had potentially faulty airspeed sensors replaced.